The present invention relates to a thermal head used as a printing element for a facsimile, a receipt printer, or the like and a thermal printer using the same, and more particularly, to a thermal printer of a type in which the thermal head and a platen roller serving as a recording medium feed mechanism member come into close contact with each other at all times and cannot be separated.
A thermal head is used as the printing element for thermal recording or thermal transfer recording performed by a facsimile, a receipt printer, or the like.
As a conventional thermal head, for example, as shown in FIG. 3, there has been known one having a structure in which on an upper surface of a heat storage layer 2 formed on a substrate 1, the heat storage layer 2 being formed of glass or the like and the substrate 1 being formed of alumina ceramics or the like, a large number of heat generating resistance layers 3 and individual electrodes 4 are arranged in a straight line, and are covered with a protective film layer 6 formed of an inorganic material such as silicon nitride or silicon oxide. While a recording medium 9 such as heat sensitive paper is allowed to slide on a surface of the protective film layer by a platen roller 8, each of the large number of heat generating resistance layers 3 is selectively caused to generate heat through electrification based on image data from outside, and the heat generated is conducted to the recording medium, thereby forming a predetermined print on the recording medium.
Note that, the protective film layer 6 serves for protecting the surfaces of the heat generating resistance layers 3, the individual electrodes 4, and a common electrode 5 from wear due to sliding with respect to the heat sensitive paper or the like, and from corrosion due to moisture or the like contained in the air. The protective film layer 6 is formed by forming a film of the inorganic material having a predetermined thickness on the surfaces of the heat generating resistance layers 3, the individual electrodes 4, and the common electrode 5 by conventional sputtering or the like.
Further, there is known a thermal head in which a fluorine-based resin is baked on the protective film layer 6 to prevent adhesion of paper dust and a conveyance failure (i.e., sticking) of the recording medium due to the adhesion of paper dust and the like.
However, a thermal head according to the above-related art, in some cases, cannot meet demands of a thermal printer including a mechanism to be described below.
In general, a thermal printer is composed of members such as a thermal head and a platen roller for conveying a recording medium while pressing the recording medium against the thermal head. As a method of inserting the recording medium between the thermal head and the platen roller, there are available a method performed when the thermal head and the platen roller are spaced apart from each other and a method performed when the thermal head and the platen roller are not spaced apart from each other. In a thermal printer having a structure in which the thermal head and the platen roller cannot be spaced apart from each other, in general, when it is recognized that the recording medium is located in proximity of the thermal head and the platen roller, the platen roller starts to rotate and the thermal head and the platen roller sandwiches the recording medium to start conveying the recording medium. However, in the thermal printer having the structure in which the thermal head and the platen roller cannot be spaced apart from each other, in a case where the thermal printer is preserved for a long period of time in a state where no recording medium is provided therein after shipment from a factory, or the like, the platen roller generally made of a rubber material may stick to the protective film of the thermal head to be fixed thereto.
In a case of the thermal head according to the above-related art, on the surface of the protective film on the heat generating resistance layers, a fluorine-based resin does not exist, so sticking partially occurs. Further, when an entire surface of a heater element portion is covered with a resin covering layer, there is a strong possibility of affecting heat generation of the thermal head, thereby deteriorating a print quality.
In such a thermal printer having the structure in which the thermal head and the platen roller cannot be spaced apart from each other, a member such as a spacer is generally interposed between the thermal head and the platen roller so that the thermal printer is prevented from being preserved without the recording medium provided therein, and the spacer is removed immediately before use.
The present invention has been made in view of the above-mentioned problem, and it is an object of the present invention to provide a thermal head and a thermal printer with which it is possible to form a fine print on a recording medium after start of printing even after a long-term preservation by preventing fixation caused by sticking between the thermal head and the platen roller to allow the recording medium to be conveyed in a stable manner.